1.4 chemical reactions and equations
TRANSCRIPT
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Physical Changes
• Do not create new substances
• Often reversible
• Four main types of physical change
1. Change of state
2. Change of shape
3. Expansion (getting bigger) or contraction (getting smaller)
4. Mixing together, dissolving
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Examples
Solid ice melting into a liquid
Wood being chopped up, changing shape
Tablet dissolving in water
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Chemical Changes
• Creates new substances
• Often not reversible
• Four main types of chemical change
1. Colour change
2. Making a gas – see bubbles, smell
3. Making a new solid (sometimes called a precipitate)
4. Releasing or absorbing energy
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Examples
Fireworks releasing heat and light energy
A nail getting rusty (rust = new solid)
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Chemical Reactions Chemical reactions require REACTANTS and create
PRODUCTS
Reactants are the chemicals that are combined together to form the Products
We write worded chemical equations like this:(combusting Hydrogen – POP TEST!)
Hydrogen + Oxygen Water
ProductsReactants
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Chemical Equations Chemical equations can be used to represent many of the
processes around us
Photosynthesis: Plants convert water and carbon dioxide to create Oxygen and Sugar:
Carbon Dioxide + Water Glucose (sugar) + Oxygen
1) What are the reactants in this reaction? What are the products?
2) If the formula for Glucose is C6H12O6, could you write the chemical equation with symbols?
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Endothermic or ExothermicCO2+ H2O C6H12O6 + O2
Chemical reactions can be exothermic or endothermic
Endothermic: The reaction absorbs energy
Exothermic: The reaction gives off energy
3) Is Photosynthesis an exothermic or endothermic reaction?
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Conservation of MassMass cannot be created or destroyed in a reaction. Therefore, the mass of the reactants must equal the mass of the products.
Translation: The number of each type of atom on each side of the equation must be the same. This makes the equation Balanced.
Hydrogen + Oxygen Water
H2 + O2 H2O
4) How many Hydrogen and Oxygen atoms on each side of the equation?
5) Is this equation balanced?
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Balancing EquationsEquations can be balanced by putting numbers (coefficients)
at the front of the formula which multiplies the number of every atom in that formula:
2H2 + O2 2H2O
Now answer:
6) How many Hydrogen and Oxygen atoms on each side of the equation?
7) Is this equation balanced?
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Balance PhotosynthesisCO2+ H2O C6H12O6 + O2
8) (HARD) This equation isn’t balanced. Try to balance it!
Hint: Balance one element at a time, start with Carbon.
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Your Turn:9) Copper and Sulphur Dioxide are combined in a reaction which forms copper sulphide and oxygen gas.
10) Our respiration (breathing) forms a reaction of Glucose (sugar) and Oxygen gas, which forms Carbon Dioxide and Water (vapour)
STEPS: Identify the reactants and products Write a word equation Write an unbalanced formula equation Balance the equation